This proposal is divided into three sections, each with a separate, specific objective. The first section of the proposal is entitled "The Surgical Treatment of Atrial Dysrhythmias" and is designed to develop new surgical techniques that will prelude the necessity for implanting artificial pacemaking systems in patients who presently require His bundle ablation for the treatment of refractory supraventricular tachycardia secondary to ectopic left atrial foci, atrial flutter/fibrillation, and A-V node re-entry. The second section of the proposal is entitled "The Surgical Treatment of Ventricular Tachyarrhythmias Associated with Ischemic Heart Disease" and is designed to clarify the electrophysiologic mechanism whereby left ventricular endocardial surgical techniques ablate ischemic ventricular arrhythmias, the effect of the surgical procedures on regional myocardial function, regional myocardial blood flow, and left ventricular structural integrity, and the development of a safe effective surgical technique for the treatment of ischemic ventricular dysrhythmias. The third section of this proposal is entitled "The Electrophysiologic Indices of Reversible Myocardial Ischemic Injury" and is designed to establish a method whereby myocardial integrity can be monitored quantitatively on a continuous basis during and after cardiac surgical procedures.